The present invention concerns a brake system for a vehicle and a method for operating a brake system for a vehicle.
In particular, agricultural vehicles can have a mechanically operated steering brake function. The steering brake function can, for example, be implemented by a dual-circuit, parallel operated brake control valve (which, for example, is implemented as a foot-operated brake valve) with a brake circuit separation into a left and a right brake circuit relative to the longitudinal axis of the vehicle and two foot-operated brake pedals. Alternatively, two separate mechanical controllers can be provided for applying pressure to the left or right rear wheel.
Furthermore, solutions for implementing a steering brake function are known, with which one or more electrical pressure control valves or shut-off valves are actuated by one or more electronic control units depending on different input information.
It is the object of the present invention to provide an improved steering brake function for a vehicle.
This object is achieved by a brake system for a vehicle and a method for operating a brake system for a vehicle according embodiments of the invention.
The approach proposed here provides a brake system for a vehicle, wherein the brake system comprises the following features:
a pneumatically and/or hydraulically operated first brake device for braking the first wheel of the vehicle;
a pneumatically and/or hydraulically operated second brake device for braking the second wheel of the vehicle;
a first brake pedal associated with the first wheel;
a second brake pedal associated with the second wheel;
a brake control valve that is designed to apply a pneumatic and/or hydraulic brake pressure to the first brake device and/or the second brake device when the first brake pedal and/or the second brake pedal is operated;
a first control valve for controlling the brake pressure in the first brake device;
a second control valve for controlling the brake pressure in the second brake device; and
an electromechanical switch module actuated by the first brake pedal and/or the second brake pedal, which is designed to activate the second control valve when the first brake pedal is actuated in order to remove or at least to reduce a braking effect of the second brake device, and/or to activate the first control valve when the second brake pedal is actuated in order to remove or at least reduce a braking effect of the first brake device.
The two brake devices can be implemented as disk brakes or drum brakes, for example. A vehicle can be a motor vehicle, in particular a commercial vehicle such as an agricultural vehicle, for example. The brake devices can be part of a rear wheel brake of the vehicle, for example. The first wheel and the second wheel can be disposed on different sides of the vehicle. For example, the two wheels can be coupled to each other by a differential gearbox. A brake control valve can be a valve that can be operated (for example by the two brake pedals), which is designed to produce either a pneumatic or a hydraulic brake pressure or both a pneumatic and also a hydraulic brake pressure in at least one of the two brake devices depending on a respective actuation travel of the brake pedals.
Depending on the embodiment, the brake devices can be coupled to the brake control valve via one or more brake circuits. The brake pedals can be operated independently of each other when the steering brake function is activated. When the steering brake function is not activated, the brake pedals can be coupled to each other mechanically. The two brake devices can each be connected to the brake control valve via at least one control valve. A control valve can, for example, be a pressure control valve or a shut-off valve, which prevents brake pressure from being applied to the respective brake device when in the activated state, so that the brake device is not activated or the brake force thereof is at least reduced despite the brake pedal being depressed. The two control valves can be electrically actuated and each can be connected to the electromechanical switch module. The electromechanical switch module can, for example, be a logic circuit with two mechanically operated switches, each of which can be mechanically coupled to one of the two brake pedals. The electromechanical switch module can, for example, be connected to a voltage source when the steering brake function is activated, so that a voltage is applied to the second control valve when the first switch is actuated by the first brake pedal or the voltage is applied to the first control valve when the second switch is actuated by the second brake pedal.
The approach presented here is based on the knowledge that it is possible to implement a steering brake function of the vehicle using an electromechanical switch module coupled to two brake pedals.
As a result, a steering brake function can also be implemented in the event of a brake circuit separation between front and rear axles or in the case of brake circuits that are disposed or operated in series, without an electrical control unit being necessary for logical control of the steering brake function.
For example, the switch module can be implemented such that only the opposite wheel is braked when an individual brake pedal is actuated by suitably shutting off or venting a brake line to a left or right rear wheel brake, and possibly a brake line to a front wheel brake. Thus, for example, the turning radius of the vehicle is reduced or a directional correction is carried out, for example during field work.
In the case of a vehicle with two brake pedals for actuating the single-circuit brake control valve or the dual-circuit brake control valve with serial brake circuits, as a rule all wheel brakes are subjected to pressure, and this is independent of which brake pedal is operated by the driver.
The steering brake function can also be implemented without the use of the control unit when using single-circuit brake control valves or dual-circuit brake control valves disposed in series by coupling the respective pressure control valves of the wheel brakes to the brake pedals by means of a simple electrical logic circuit. Such a circuit gives the advantage of low manufacturing costs and a high degree of robustness against ambient influences.
According to one embodiment, the brake system can comprise at least a first brake circuit and a second brake circuit. The brake control valve can be implemented to apply the brake pressure to the first brake device either via the first or the second brake circuit or via both brake circuits. The brake control valve can be implemented to further apply the brake pressure to the second brake device either via the first or the second brake circuit or via both brake circuits. In particular, the first and the second brake circuits can be connected in series. A brake circuit can mean a line circuit for passing the brake pressure into at least one of the two brake devices. The brake circuits can be mutually independent. By the use of two brake circuits, the probability of the total failure of the brake system can be reduced.
It is advantageous if the brake system comprises at least one pneumatically and/or hydraulically operated further brake device for braking at least one further wheel of the vehicle and at least one further control valve for controlling the brake pressure in the further brake device. In this case, the brake control valve can be designed to also apply the brake pressure to the further brake device when at least one of the two brake pedals is actuated. Accordingly, the switch module can be implemented to also activate the further control valve when at least one of the two brake pedals is actuated in order to remove or at least reduce a braking effect of the further brake device. The further brake device can be a front wheel brake of the vehicle, for example. As a result, the steering brake function can be implemented with low added cost, even in the case of using more than two brake devices.
According to a further embodiment, the brake control valve can be implemented to apply the brake pressure to the first brake device via the first brake circuit. In addition or alternatively, the brake control valve can be implemented to apply the brake pressure to the second brake device via the second brake circuit. As a result, the first and the second brake devices can be subjected to the brake pressure independently of each other, so that in the event of a failure of one brake device, the other brake device continues to be operational. For example, a circuit separation between left and right sides of the vehicle can be achieved with said embodiment.
It is further of advantage if the switch module comprises a first control port that is electrically conductively connected to the first control valve, a second control port that is electrically conductively connected to the second control valve, a supply port for applying a supply voltage, a first switch that is mechanically coupled to the first brake pedal and a second switch that is mechanically coupled to the second brake pedal. In this case, the first switch can be implemented to electrically conductively connect the second control port to the supply port when the first brake pedal is actuated in order to activate the second control valve. Similarly, the second switch can be implemented to electrically conductively connect the first control port to the supply port when the second brake pedal is actuated in order to activate the first control valve. To apply the supply voltage, the supply port can be coupled to the voltage source. Such a switch module can be provided particularly inexpensively and gives the advantage of high reliability owing to the simple mechanical embodiment thereof. As a result of the actuation of the switch being carried out in a purely mechanical way, the use of the control unit can be dispensed with, whereby the manufacturing costs of the brake system can be reduced.
The switch module can comprise at least one further control port that is electrically conductively connected to the further control valve and, in addition or alternatively, to a trailer control valve for controlling the brake pressure in a pneumatically and/or hydraulically operated trailer brake device for braking the trailer of the vehicle. In this case, the first switch can be implemented to electrically conductively connect the further control port to the supply port when the first brake pedal is actuated. The second switch can be implemented to electrically conductively connect the further control port to the supply port when the second brake pedal is actuated. Depending on the embodiment, when connecting the supply port to the further control port, either the further control valve or the trailer control valve or both the further control valve and also the trailer control valve can be activated to remove or at least reduce a braking effect of the further brake device or the trailer brake device. As a result, the switch module can be used for actuating a plurality of control valves at low additional cost.
The brake system can be provided with at least one trailer switch that is disposed between the further control port and the trailer control valve for controlling a voltage supply of the trailer control valve. The trailer switch can, for example, be a relay or another electromechanical switch. For example, the trailer switch can be operated by a driver of the vehicle. By means of the trailer switch, a voltage supply of the trailer control valve can be interrupted independently of a position of the first and second switches. As a result, it can be ensured that the trailer can also be braked when the steering brake function is activated.
The switch module can be implemented in a particularly simple, reliable and inexpensive version if a first diode with a conducting direction from the first control port to the further control port is disposed between the first control port and the further control port and a second diode with a conducting direction from the second control port to the further control port is disposed between the second control port and the further control port. In this case, the first control port, the second control port and the further control port can be connected in series. By means of the diodes, it can be prevented that the supply voltage is applied to the first and the second control ports at the same time and thus that the first and the second control valves are activated at the same time, i.e., by means of the diodes it is guaranteed that the supply voltage is either only applied to the first and further control ports or only to the second and further control ports.
Furthermore, the first and the second switches can be connected in series. The second switch can be implemented to electrically conductively connect the second control port to the first switch in a rest position of the second brake pedal. The first switch can be implemented to electrically conductively connect the first control port to the second switch in a rest position of the first brake pedal. A rest position can be a position of the brake pedal when the brake system is not activated. This embodiment enables at least the second control port to be coupled to the supply port owing to the sole actuation of the first switch and at least the first control port to be coupled to the supply port owing to the sole actuation of the second switch. This enables additional measures for synchronizing the two switches to be omitted.
According to a further embodiment, the brake system can comprise a control unit for controlling a voltage supply of the switch module. In particular, the control unit can be implemented to interrupt the voltage supply if the vehicle exceeds a predetermined speed. Depending on the embodiment, the control unit can, in addition or alternatively, be implemented to interrupt the voltage supply if the vehicle exceeds a predetermined tilt angle, a differential lock of the vehicle is activated or a trailer is coupled to the vehicle. As a result, the driving stability of the vehicle can be increased when the steering brake function is activated.
A control unit can be an electrical unit that processes sensor signals and depending thereon outputs control and/or data signals. The control unit can have an interface that can be implemented in hardware and/or software. In the case of a hardware implementation, the interfaces can be, for example, part of the so-called system ASIC, which contains diverse functions of the control unit. It is however also possible that the interfaces are dedicated integrated circuits or at least partly consist of discrete components. In the case of a software implementation, the interfaces can be software modules that are present in a microcontroller with other software modules, for example.
Finally, the approach presented here provides a method for operating a brake system according to any one of the embodiments. The method comprises a step of outputting the control signal to the second control valve through the switch module if the first brake pedal is actuated in order to remove or at least reduce the braking effect of the second brake device. In addition or alternatively, in the outputting step a control signal can be output to the first control valve through the switch module if the second brake pedal is actuated in order to remove or at least reduce the braking effect of the first brake device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In the following description of the preferred exemplary embodiments of the present invention, the same or similar reference characters are used for similarly acting elements that are represented in the different figures, wherein a repeated description of said elements is omitted.